1. Field of the Invention
The present invention relates generally to the field of read channel equalization in a magnetic recording device and in particular to a read equalization level control in a tape drive.
2. Description of the Related Art
Magnetic recording devices such as magnetic tape drives are used for recording computer data for storage and retrieval. Various techniques have been developed over the years to improve the characteristics of data reading and writing on magnetic media.
On the read channel side, Finite Impulse Response (FIR) filters are widely used as a means of equalizing the read channel response to a given target response, for example PR4, EPR4, or the like. The response of these filters is controlled by a set of coefficients. Often the response of the FIR filter is changed during the operation of the tape drive in order to compensate for changes in channel characteristics, for example, changes in the recording media, the recording head, the electronics, and the like. Tape drives in particular must deal with the variations in the channel characteristics caused by the interchange of the recording media.
A general method for changing the FIR filter coefficients in order to optimize the FIR filter responses is by implementing LMS (Least Mean Square) hardware adaptability. The LMS algorithm needs a coefficient set as a starting point. Importantly, this starting point must be good enough to detect data in order for the LMS algorithm to have a valid input on the ideal sample values. Further, the LMS coefficients may develop by themselves to be unsuitable for data detection during changes in channel response, for example in dropout situations. This can result in a deadlock situation occurring.
The prior art devices provide that, when starting the data detection, the starting point for the coefficients of the FIR filter by the channel control system may be embedded in firmware. This starting point for the coefficients is also provided when a deadlock situation is detected.